The present invention relates to a controlled-release additive composition for use in water treatment systems, particularly coolant and hot water systems, for example, engine coolant systems, and to a method of using said additive compositions. The controlled release additive composition comprises a water-soluble core containing at least one water treatment chemical and a polymeric coating material encapsulating said core which slowly releases the water treatment chemical into the water treatment system, thereby delivering an effective level of the water treatment chemical to the water treatment system over an extended period.
Traditionally, additives such as anti-foulants, anti-scaling agents, corrosion inhibitors, buffering and pH agents, microcides and the like are added directly to water treatment systems as needed to prevent scale deposition, corrosion of metal surfaces and similar fouling of water treatment systems, as well to maintain proper pH levels. Typically, a system is monitored, such as by recovering and analyzing a sample, in order to determine the current level of particular chemical treatment agents. When the concentration of a particular agent falls below a desired level, additional agent is added to the system.
Similar methods have been employed for treating coolant systems. For example, the use of conventional antifreeze alone is sometimes insufficient to meet the demands of engine coolant systems. As a result, coolant additives (CA) are added to engine coolant systems to make up for the deficiencies of antifreeze formulations. Typically, coolant additives are added to the engine coolant system at each oil change in order to replace additives which have been diluted or depleted from the system.
Various methods of introducing coolant additives to the engine coolant system have been developed. For instance, a solid CA material may be added directly to the engine coolant system which dissolves in the coolant system. However, this method cannot maintain a steady concentration level of coolant additives within the system. Initially, there would be a high level of the coolant additives released into the system, and within a short time the coolant additives are depleted. Additionally, a significant draw back of this method is the danger of overdosing the system with particular additives which are initially released. The overdosing is dangerous in that it can result in erosion and corrosion problems.
Other attempts to have a good delivery of coolant additives to an engine system include the use of coolant filters which contain coolant additives. These devices operate as bypass filters with coolant flowing through the filter and extracting the coolant additive thereby. Although the use of coolant filters is an improvement over the use of a coolant additive block, the danger of overdosing still exists. For example, recently, there has been an interest in dramatically extending the coolant service interval from the typical two months interval to a once-a-year interval. This in turn increases the interval mileage from 15,000-20,000 miles up to approximately 120,000 miles, or more. Consequently, more additive must be placed into the filter to accommodate the longer time interval. However, the large amount of additive results in a high level of initial release, which is directly related to the creation of certain undesirable side effects to the coolant system, as discussed previously. Furthermore, the use of coolant filters failed to maintain a minimum level of coolant additives within the system.
Minimal attempts have been made in the prior art to address particular water treatment systems by using controlled release coatings. For example, Characklis in U.S. Pat. No. 4,561,981 (issued Dec. 31, 1985) disclosed a method for controlling, preventing or removing fouling deposits, particularly in pipelines, storage tanks and the like by mircroencapsulating fouling control chemicals in a slow release coating. The coating material is described as being any material compatible with the fouling control chemical which is capable of sticking to the fouling deposit site. However, the coating materials as disclosed by Characklis may dissolve in an engine coolant system and create further corrosion problems.
Recently, Mitchell et al. in U.S. Pat. No. 6,010,639 disclosed that a terpolymer may be used as a coating for coolant additives.
However, despite the efforts of the prior art, a need still exists for a controlled release coolant treatment composition.
Accordingly, the present invention provides a controlled release additive composition for water treatment systems. This invention provides for delayed and more effectively complete release of treatment additive components, to maintain a consistent level of treatment additive components in the water system over an extended period of time. Preferably, the treatment additive components are coolant additive components. Additionally, the water system is preferably a coolant system.
More particularly, the present invention provides a controlled release coolant additive composition for engine coolant systems which slowly releases one or more coolant additive (CA) components into the engine coolant system.
In one embodiment, a controlled release coolant composition has a core containing a water-soluble coolant additive component and a coating substantially surrounding the core.
In a preferred embodiment, the coating is a polymer made up of units from no more than two monomers. More preferably, the units include vinylacetate and vinyl versatate.
The coolant additive component has at least one active ingredient selected from the group consisting of buffering components, captivation liner pitting inhibitors, metal corrosion and hot surface corrosion inhibitors, defoaming agents, hot surface deposition, scale inhibitors, dispersant agents, organic acids, surfactants and mixtures thereof.
In a preferred embodiment, the coolant additive component also includes sodium nitrite, sodium nitrate and sodium molybdate.
In another embodiment, a method is provided for maintaining an effective concentration of at least one engine coolant additive component in an engine coolant system. The method includes steps of circulating the coolant of the system through a filter which contains the controlled release coolant additive composition.
Each and every feature described herein, and each and every combination of two or more of such features, is included within the scope of the present invention provided that the features included in such a combination are not mutually inconsistent.
The present invention relates to a controlled release coolant additive composition for use in coolant or hot water systems, particularly for use in engine coolant systems. The controlled release coolant additive (CA) composition comprises a core containing a water-soluble coolant additive component and a coating encapsulating said core which enables the slow release of the coolant additive component into the engine coolant system. Any type of coating conventionally known in the art which provides controlled-release properties may be used in the present invention.
In a preferred embodiment, the coating is a polymer dispersion. More preferably, the polymer dispersion has the following properties:
1. Low viscosity: The polymer dispersion should be of a low to medium viscosity. When the viscosity is too high, it would become impossible to pump the polymer dispersion through a coating system. This would cause the line and spray gun to become plugged. Also, in this case, the droplets of polymer dispersion would be too thick and difficult to lose moisture. They would not have the desired level of dryness before they reach the tablet surface. Therefore, the polymer would not form a good and homogeneous coating.
It should be noted that reducing the viscosity of a polymer dispersion through dilution with water is not always a viable solution. Often the dilution leads to changes of physical properties for the polymer dispersion and renders the polymer not appropriate for coating applications.
2. Low film forming and glass transition temperatures: Every polymer has its own characteristic film forming temperature and glass transition temperature, Tg. To form a good coating, the polymer must have a film forming temperature lower than the operating temperatures inside the chamber of the drum coater in the coating process. A high Tg would lead to a brittle and fragile film which may easily peel off. Generally, a polymer with lower film forming temperature and Tg forms better film than those polymers with higher corresponding temperatures.
3. Good film forming ability onto tablet surface: In the early stage of coating process, the polymer has to have good adherence to the tablet surface, so that the coating film can gradually build up. The polymer particles should pack well without large spaces or holes in between. This can be examined and confirmed under a microscope. Typically the polymer with small particle size will result in better packing. Also, the polymer must possess good elasticity; otherwise, the coating would crack, especially upon cooling.
4. Insolubility of the polymer in coolants under engine operating conditions: Typically the engine coolants are composed of water and ethylene glycol in equal volumes with a pH of 7.0 to 11.0 and operating temperatures of 170 degrees F to 210 degrees F. These are very demanding conditions for polymer coatings to remain insoluble and stable for 1,000 hours or longer.
If the polymer coating dissolves in coolant solutions, it will lose the slow release function. Moreover, polymer deposits on the engine metal surfaces may be detrimental to the engine. Therefore, it is preferred that the polymer is insoluble in coolant solutions.
5. Stability of polymer coating in coolants under engine operating conditions: Many polymers degrade because they undergo alkaline hydrolysis reaction in coolants under engine operating conditions. As degradation or dissolution occurs, the coating is damaged. As a result, the coating forms holes and loses the control of slow release. Subsequently, all chemical ingredients rapidly enter the bulk coolant.
6. Good release rates for ingredients: The release must be gradual, effective and substantially complete preferably at about 500 service hours (20,000 miles), more preferably about 1,000 service hours (40,000 miles) and even more preferably about 2,500 service hours (100,000 miles) or longer.
Without wishing to limit the invention to any particular mechanism or theory of operation, it is believed that the release of ingredients from the tablet core into the bulk coolant solution involves three steps: (a) coolant solution enters the inner tablet core through the polymer.coating, (b) chemical ingredients of the tablet dissolve in contact with coolant and (c) the resulting highly concentrated solution diffuses through the polymer coating back into the bulk coolant. The path and size of channels, microscopically, within the polymer coating, which are characteristics of each specific polymer and are closely related to the physical properties of each polymer in coolant solutions at elevated temperatures, control the kinetics of these actions.
In one embodiment, film forming polymers are found to have these desired properties. Suitable film forming polymers include, for example, homopolymers, copolymers and mixtures thereof, wherein the monomer units of the polymers are preferably derived from ethylenically unsaturated monomers.
A particularly useful ethylenically unsaturated monomer is compound I with the formula (R1) (R2) (R3)Cxe2x80x94COOxe2x80x94(CHxe2x95x90CH2), wherein R1, R2 and R3 are saturated alkyl chains. In one embodiment, R3 of compound I is CH3, and R1 and R2 of compound I have a total of about 2 to about 15 carbons; such a molecule is also known as a vinylversatate. In a preferred embodiment, R3 is CH3, and R1 and R2 have a total of about 5 to about 10 carbons. In a more preferred embodiment, R3 is CH3, and R1 and R2 have a total of 7 carbons., i.e. R1+R2=C7H16.
In another embodiment, each of the R1, R2, and R3 of compound I is a single chemical element. For example, the element may be a halogen, preferably a chloride. More preferably, the element may be a hydrogen. Compound I having a hydrogen as the element for R1, R2 and R3 is known as vinylacetate.
In another embodiment, R1 of compound I may be a single chemical element, and R2 of compound I may be a saturated alkyl chain.
Other examples of ethylenically unsaturated monomers include: Monoolefinic hydrocarbons, i.e. monomers containing only carbon and hydrogen, including such materials as ethylene, ethylcellulose, propylene, 3-methylbutene-1, 4-methylpentene-1, pentene-1, 3,3-dimethylbutene-1, 4,4-dimethylbutene-1, octene-1, decene-1, styrene and its nuclear, alpha-alkyl or aryl substituted derivatives, e.g., o-, - or p-methyl, ethyl, propyl or butyl styrene, alpha-methyl, ethyl, propyl or butyl styrene; phenyl styrene, and halogenated styrenes such as alpha-chlorostyrene; monoolefinically unsaturated esters including vinyl esters, e.g., vinyl propionate, vinyl butyrate, vinyl stearate, vinyl benzoate, vinyl-p-chlorobenzoates, alkyl methacrylates, e.g., methyl, ethyl, propyl, butyl, octyl and lauryl methacrylate; alkyl crotonates, e.g., octyl; alkyl acrylates, e.g., methyl, ethyl, propyl, butyl, 2-ethylhexyl, stearyl, hydroxyethyl and tertiary butylamino acrylates, isopropenyl esters, e.g., isopropenyl acetate, isopropenyl propionate, isopropenyl butyrate and isopropenyl isobutyrate; isopropenyl halides, e.g., isopropenyl chloride; vinyl esters of halogenated acids, e.g., vinyl alpha-chloroacetate, vinyl alpha-chloropropionate and vinyl alpha-bromopropionate; allyl and methallyl compounds, e.g., allyl chloride, ally alcohol, allyl cyanide, allyl chlorocarbonate, allyl nitrate, allyl formate and allyl acetate and the corresponding methallyl compounds; esters of alkenyl alcohols, e.g., beta-ethyl allyl alcohol and beta-propyl allyl alcohol; halo-alkyl acrylates, e.g., methyl alpha-chloroacrylate, ethyl alpha-chloroacrylate, methyl alphabromoacrylate, ethyl alpha-bromoacrylate, methyl alpha-fluoroacrylate, ethyl alpha-fluoroacrylate, methyl alpha-iodoacrylate and ethyl alpha-iodoacrylate; alkyl alpha-cyanoacrylates, e.g., methyl alpha-cyanoacrylate and ethyl alpha-cyanoacrylate and maleates, e.g., monomethyl maleate, monoethyl maleate, dimethyl maleate, diethyl maleate; and fumarates, e.g., monomethyl fumarate, monoethyl fumarate, dimethyl fumarate, diethyl fumarate; and diethyl glutaconate; monoolefinically unsaturated organic nitriles including, for example, fumaronitrile, acrylonitrile, methacrylonitrile, ethacrylonitrile, 1,1-dicyanopropene-1, 3-octenonitrile, crotononitrile and oleonitrile; monoolefinically unsaturated carboxylic acids including, for example, acrylic acid, methacrylic acid, crotonic acid, 3-butenoic acid, cinnamic acid, maleic, fumaric and itaconic acids, maleic anhydride and the like. Amides of these acids, such as acrylamide, are also useful. Vinyl alkyl ethers and vinyl ethers, e.g., vinyl methyl ether, vinyl ethyl ether, vinyl propyl ether, vinyl n-butyl ether, vinyl isobutyl ether, vinyl 2-ethylhexyl ether, vinyl-2-chloroethyl ether, vinyl propyl ether, vinyl n-butyl ether, vinyl isobutyl ether, vinyl-2-ethylhexyl ether, vinyl 2-chloroethyl ether, vinyl cetyl ether and the like; and vinyl sulfides, e.g., vinyl beta-chloroethyl sulfide, vinyl beta-ethoxyethyl sulfide and the like. Other useful ethylenically unsaturated monomers are styrene, methyl methacrylate, and methyl acrylate.
In one embodiment, the polymer forming the coating is made up of a copolymer of vinylacetate and vinylversatate. In a preferred embodiment, about 45% to about 90% by weight of the units are from vinylacetate and about 10% to about 55% by weight of the units are from vinylversatate. In more preferred embodiment, about 65% by weight of the units are from vinylacetate and about 35% by weight of the units are from vinylversatate.
In one preferred embodiment, the vinylversatate used is sold under the trademark VEOVA 10 sold by Shell Chemicals. In a particularly preferred embodiment, the water-based emulsion polymer is a vinylacetate-vinylversatate copolymer, sold under the trademark EMULTEX VV575 sold by Harlow Chemical Co. (England). Additionally, a surfactant may also be added to stabilize the dispersion. In a preferred embodiment, the polymer solid in the dispersion is about 54% to about 56% by weight of active polymer solid.
EMULTEX VV575 is particularly advantageous because it meets all of the six requirements for a good coating as set forth above. That is, it (1) exhibits a viscosity low enough for coating processing without difficulties, (2) has a film forming temperature of 10 degrees C and a glass transition temperature, Tg, of 11 degrees C, low enough for forming a.good coating, (3) has a fine to medium particle size of 0.37 micron and forms an elastic coating, (4) is insoluble in coolants at operating engine conditions, (5) is stable in coolants at operating engine conditions and (6) gives excellent release rates for ingredients, preferably ingredients in DCA-4+tablets.
Another preferred copolymer for coating is made up of acrylate-vinylversatate. NeoCAR 820 sold by Union Carbide is the preferred acrylate-vinylversatate copolymer used for forming coatings.
In another embodiment, the polymer for coating is made up of a homopolymer. In a preferred embodiment, the monomer unit of the homopolymer is ethylcellulose. In a more preferred embodiment, ethylcellulose used for forming coatings is purchased from Dow Chemical sold under the trademark ETHOCEL S10, S20, S100, and preferably S45.
ETHOCEL has the following molecular structure, wherein xe2x80x9cEtxe2x80x9d is C2H5: 
Specific properties of the various ETHOCEL""s are determined by the number of anhydrous units in the polymer chain (expressed by the molecular weight or the solution viscosity), and, the degree of ethoxyl substitution (expressed as the percent of hydroxyl group, xe2x80x94OH, in cellulose substituted by ethoxyl group, xe2x80x94OC2H5). The preferred ETHOCEL S45 has a solution viscosity of about 41 to about 49 cP and about 48 to about 49.90%. ethoxyl content. The viscosity is for a 5% solution in 80/20 toluene/ethanol measured at 25 degrees C in an Ubbelohde viscometer.
The CA component comprises a mixture of conventional inhibiting and buffering agents typically used in engine coolant systems. Preferably, the CA component comprises (1) a buffering component to maintain a neutral or alkaline pH, including for example, alkali metal salts or sodium phosphates, borates and the like, (2) a cavitation liner pitting inhibitor component, including for example, alkali metal or sodium nitrites, molybdates and the like, (3) a metal corrosion and hot surface corrosion inhibitor component, including for example, alkali metal and.sodium nitrates and silicates, carboxylic acids, azoles, sulfonic acids, mercaptobenzothiazoles, metal dithiophosphates and metal dithiocarbonates (one particular corrosion inhibitor that has been found to be highly, satisfactory and is preferred is a phenolic anti-oxidant, 4,4xe2x80x2-methylenebis (2,6-di-tertbutylphenol) that is commercially available under the trademark Ethyl 702 manufactured by Ethyl Corporation), and the like, (4) a defoaming agent component including for example, silicone defoamers, alcohols such as polyethoxylated glycol, polypropoxylated glycol or acetylenic glycols and the like, (5) a hot surface deposition and scale inhibitor component including for example, phosphate esters, phosphino carboxylic acid, polyacrylates, styrene-maleic anhydride copolymers, sulfonates and the like, (6) a dispersing component, including for example, non-ionic and/or anionic surfactants such as phosphate esters, sodium alkyl sulfonates, sodium aryl sulfonates, sodium alkylaryl suilfonates, linear alkyl benzene sulfonates, alkylphenols, ethoxylated alcohols, carboxylic esters and the like, (7) an organic acid, including for example adipic acid, sebacic acid and the like, (8) an anti-gel such as that disclosed by Feldman et al in U.S. Pat. No. 5,094,666, the content of which is incorporated in its entirety herein by reference (for example, such anti-gel additive comprises copolymers of ethylene and vinyl esters of fatty acids with molecular weight of 500-50,000; or Tallow amine salt of phthalic anhydride, used at 0.01-0.2; or Tallow amine salt of dithio benzoic acid, used at 0.005-0.15%; or 4-hydroxy, 3,5-di-t-butyl dithiobenzoic acid; or ethylene-vinylacetate copolymers).
Typical CA components contain a mixture of one or more of the active components provided in the following Table 1.
In one embodiment, the CA component includes nitrite compounds. In a preferred embodiment, the CA component includes a mixture of nitrite compounds and molybdate compounds to maintain a minimum concentration level of about 800 ppm of nitrite or a mixture of nitrite and molybdate in the coolant system, with the proviso that the minimum level of nitrite in the coolant system is about 400 ppm. Such additive is sold by Fleetguard under the trademark DCA-2+, which includes borate, silicate, organic acids, tolytriazole, scale inhibitors, surfactants and defoamers, in addition to nitrite and molybdate.
In a more preferable embodiment, the CA component includes a mixture of nitrite, nitrate and molybdate compounds. In a more preferred embodiment, the CA additive component comprises nitrite, nitrate, phosphate, silicate, borate, molybdate, tolyltriazole, organic acids, scale inhibitors, surfactants and defoamer. Such an additive is sold by Fleetguard under the trademark DCA-4+.
The CA component may be in solid, granular or particulate form provided that it does not decompose or melt at processing temperatures. Preferably, the CA component is molded in the form of a pellet or tablet which may have either a spherical or irregular shape. The CA pellet or tablet should be of sufficient size to provide the steady controlled release of the CA components into the coolant system over the desired period of time. Further, when the CA pellet or tablet is used in a filtering environment, it should be larger than the pores or orifices of the filter. Generally, a spherical pellet or tablet should have a diameter on the order of from about {fraction (1/32)}xe2x80x3 to about 3.0xe2x80x3, preferably from about {fraction (1/32)}xe2x80x3 to about xc2xdxe2x80x3, and more preferably from about xe2x85x9xe2x80x3 to about xc2xdxe2x80x3. An irregularly shaped pellet or tablet should be on the order of from about {fraction (1/16)}xe2x80x3 times {fraction (1/16)}xe2x80x3 to about 3.0xe2x80x3 times 3.0xe2x80x3, preferably from about xe2x85x9xe2x80x3 times xe2x85x9xe2x80x3 to about 1.5xe2x80x3 times 1.5xe2x80x3 and more preferably from about {fraction (3/16)}xe2x80x3 times {fraction (3/16)}xe2x80x3 to about xc2xdxe2x80x3 times xc2xdxe2x80x3.
The formation of the CA component into a pellet or tablet is dependent upon the mixture of materials contained therein. For example, when the CA component contains a sufficient amount of a dispersing agent or a mixture of dispersing agents, the dispersing agent or mixture also may function as a binder, thereby allowing the component to be molded or compressed directly into the form of a pellet or tablet. If the CA component does not compact well, a binder must be added to the CA component in order to mold or compress it into a pellet or tablet. Suitable binders include, for example, polyvinyl pyrrolidone, sodium acrylate, sodium polyacrylate, carboxymethylcellulose, sodium carboxyinethylcellulose, corn starch, microcrystalline cellulose, propylene glycol, ethylene glycol, sodium silicate, potassium silicate, methacrylate/acrylate copolymers, sodium lignosulfonate, sodium hydroxypropylcellulose, preferably hydroxyethylcellulose, and water.
Preferably, the CA component to be molded or compressed into a pellet or tablet further comprises a die release agent. Suitable die release agents include, for example, calcium stearate, magnesium stearate, zinc stearate, stearic acid, propylene glycol, ethylene glycol, polyethylene glycol, polypropylene glycol, polyoxypropylene-polyoxyethylene block copolymers, microcrystalline cellulose, kaolin, attapulgite, magnesium carbonate, fumed silica, magnesium silicate, calcium silicate, silicones, mono-and dicarboxylic acids and corn starch.
To form a controlled release coolant additive composition, the polymeric coating may be applied to the CA composition core by spray coating, microencapsulation or any other coating technique well known to practitioners in the art. Preferably, the polymeric coating is an aqueous dispersion latex which is applied to the CA core pellet or tablet by drum or pan coating. The amount of coating to be applied to the CA core is dependent upon the desired controlled release characteristics of the resulting coated tablet or pellet. An increase in the amount of coating will result in a decrease of the rate of release of the CA component. Preferably, the weight percent of the coating is from about 1.0 to about 40.0% based on the total weight of the CA tablet, more preferably from about 2% to about 37% by weight and most preferably from about 10 to about 35% by weight.
In one broad embodiment, a method is provided for maintaining an effective concentration of at least one engine coolant additive component in an engine coolant system. The method includes steps of placing the coolant additive composition, such as the ones described herein, in contact with the engine coolant. Although the coated CA tablets or pellets may be introduced directly into the coolant system, such a delivery method can result in the polymeric coating itself fouling the system. In order to prevent the water insoluble polymeric coating from being introduced into the coolant system along with the CA additive, the coated tablets are placed within a filtering environment such that the filter can release the water-soluble CA component into the coolant system but trap and retain the larger particles of polymeric coating. The selection of such a filtering environment is dependent on whether the coolant system is a circulating or non-circulating system. In circulating systems such as engine coolant systems, coolant filters currently are being utilized in order to introduce chemical coolant additives to the cooling system. An example of such a filter device is the WF2171 Coolant filter, sold by Fleetguard.
The following non-limiting examples illustrate certain aspects of the present invention.